(1) Field of the Invention
This invention relates to attenuating phase shifting masks and the use of attenuating phase shifting masks to achieve increased depth of focus for widely spaced line/space patterns on the same mask as dense line/space patterns.
(2) Description of the Related Art
The depth of focus achieved using binary masks to form parallel line/space patterns is adequate when the density of the line/space patterns is high and the lines are closely spaced. For isolated lines or widely spaced line/space patterns the depth of focus achieved with binary masks is not adequate. Scattering bar patterns can be used in regions having isolated lines or widely spaced line/space patterns but this complicates the fabrication and inspection of the mask.
Attenuating phase shifting masks can be used to improve the depth of focus for isolated lines or widely spaced line/space patterns but dense line/space patterns can not be resolved with attenuating phase shifting masks using a bias even with a very high numerical aperture setting because of the transmittance through the attenuating phase shifting material.
U.S. Pat. No. 5,565,286 to Lin describes a structure and fabrication method for a mask using an attenuating phase shifting mask in combination with an alternating element phase shifting mask.
U.S. Pat. No. 5,786,114 to Hashimoto describes attenuating phase shifting masks with a halftone layer used to form boundary regions such as an inter-chip regions or kerf regions.
U.S. Pat. No. 5,795,682 to Garza describes attenuating phase shifting masks using a compensating transmissive region located where side lobe effects are expected to be most severe.
U.S. Pat. No. 5,766,804 to Spence and U.S. Pat. No. 5,766,806 to Spence describes the use of phase shifting masks showing assignment rules for phase assignment for the phase shift masks.